PAULSBORO, NJ — There may have been a problem with a signal at a New Jersey bridge just before a trail derailed there, spewing a hazardous chemical into the air that sickened dozens of people.

National Transportation Safety Board chairman Deborah Hersman said Saturday that train crewmembers have told investigators that a radio code used to change a light from red to green failed to work just before Friday’s accident.

The conductor got out of the train and visually inspected the bridge in Paulsboro, she said. The crew then called for and received permission to cross, she said.

It’s unclear if the malfunctioning signal had anything to do with the accident, she said. Hersman said the train was moving 8 mph just before seven cars derailed on the bridge — below the 10 mph speed limit.

More than 100 people in southern New Jersey remained out of their homes Saturday as officials continued their efforts to clear a hazardous gas that spewed from a ruptured freight train car.

The precautionary evacuations in Paulsboro were ordered late Friday, hours after the train derailment, and will likely remain in effect throughout the weekend and possibly longer.

The order came after readings showed higher levels of vinyl chloride in the air. The gas, used to make the common plastic PVC, can make people dizzy or sleepy.

A Conrail spokesman said his company was paying for 106 hotel rooms for displaced residents. He was not certain how many people had been told to leave.

Meanwhile, officials continued the delicate cleanup and investigation that started after the train derailed, sending four tanker cars partially into a creek.

Speaking at a news conference Saturday morning, Coast Guard Capt. Kathy Moore said crews would “exclusively be working” on removing the remaining chemicals, now in a solid state, out of the breached car.

Moore said there were no signs that any of the other train cars had been ruptured, but added “there’s still a lot we don’t know.”

National Transportation Safety Board members arrived Friday to start the work of piecing together how the accident happened on the swing-style rail bridge where there was another derailment three years ago. With increased health concerns close to the site, Hersman said her investigators would initially focus on reviewing records, interviewing witnesses and other parts of the investigation that can be done away from the accident scene.

Meanwhile, local authorities said the job of lifting tanker cars was so immense that no cranes in the Philadelphia area were strong enough to handle it. One was being floated in by barge from New York Harbor — a full day’s journey away — for the job.

While the machinery is big, the operation must be precise to avoid any further ruptures to derailed cars.

The derailment happened at about 7 a.m. Friday in Paulsboro, an industrial town directly across the Delaware River from Philadelphia International Airport. The train — two locomotives, 83 freight cars and a caboose — was making its way from Camden when seven cars derailed. Five of them were on the bridge and two were nearby.

Four of the tankers were filled with vinyl chlorine. One of those cars ruptured, spewing some of the gas into the air.

The gas can make people dizzy or sleepy. Breathing very high levels can cause someone to pass out, and breathing extremely high levels can cause death. Most of the vinyl chloride is gone from the body one day after being breathed in.

More than 70 people who live or work in the area went to an emergency room, but none were found to have life-threatening conditions and most were discharged within hours.

The bridge was rebuilt after it buckled in August 2009 when nine cars carrying coal derailed. Officials blamed bridge misalignment for that accident.

Hersman said Friday that her agency will not rule on a cause during its initial, on-the-ground investigation.

On Friday, 17 NTSB workers were in Paulsboro starting to assess the integrity and history of the bridge, the mechanics of the train and the condition of its crew.

She said the cars would be moved only after they’d been documented.

For the ruptured one, the major concern was dealing with the solidified vinyl chlorine that remained inside. Tom Butts, chief of the Gloucester County Office of Emergency Management, said the chemical could be sprayed with water, which would turn it into gas, and then more water could be used to neutralize it as it dissipates into the air. But Hersman said the method of removing the vinyl chloride was not decided for certain.

Local authorities said residents should remain cautious and heed official announcements in case more of the gas gets into the air during the cleanup.

Assemblyman John Burzichelli, a former mayor of Paulsboro who was acting as the town’s spokesman on Friday, said getting the rail fixed and reopened is important for commerce in a stretch of New Jersey with refineries and factories.

“This is heavy rail and this is heavy freight,” he said.

As long as the bridge is out, he said, businesses will have to rely on barges and trucks to move goods.